Directed ortho Lithiation of Sulfonylazulenes. An Efficient Method to Introduce Substituents at the 2-position of Azulene

Abstract

2-Lithioazulenes were successfully synthesized from 1-azulenyl p-tolyl sulfone 3 and N, N-diethyl 1-azulenylsulfonamide 4 by using
directed ortho metallation with a directing sulfonyl group. Proton abstraction at the 2-position of azulenes was done by using lithium
2,2,6,6-tetramethylpiperidide (LTMP). The azulenyllithiums thus obtained from 3 and 4 were effectively transformed into 2-substituted
azulenes in moderate to good yields by trapping with electrophiles.